The present invention relates to a golf club shaft made of fiber-reinforced-plastic (FRP).
A golf club shaft is generally constructed such that a plurality of prepreg sheets of carbon fiber-reinforced plastic (CFRP) are rolled onto an elongated mandrel to form a rolled assembly of sheets which is heat-treated to cure and form a hollow shaft from which the mandrel is removed. The prepreg sheet is made from unidirectional carbon fibers and the golf club shaft generally comprises longitudinal layers containing fibers oriented approximately parallel to a longitudinal axis of the shaft and biased layers containing fibers oriented at a substantial angle transverse to the longitudinal axis of the shaft.
Such carbon shaft is lighter than a steel shaft. Further, much attention has been focused on a reduction in the number of turns of prepreg sheets, in order to provide a lighter carbon shaft. However, simply reducing the number of turns of prepreg sheets causes a player to only feel the club is light without sensing the weight of the club head at the end of the shaft. This leads to a problematic situation where the swing orbit of a club head during a player's swing is destabilized and the player is not able to swing a golf club easily and/or has an inconsistent shot pattern.
Japanese Unexamined Patent Publication No. 2000-14844 discloses a light-weighted golf club shaft in which a biased layer is formed by using a prepreg sheet of super-elastic alloy fibers to achieve a longer driving distance and to give a player a lot more consistent shot pattern. Japanese Unexamined Patent Publication No. 2002-282399 discloses a golf club shaft which is constructed so that a hoop layer containing fibers oriented perpendicular to a longitudinal axis of the shaft is formed in the butt-end portion of the shaft to allow the shaft to have high collapse resistance and allow a player to have a good feel for the shaft and a longer driving distance